1. Field of the Invention
The present invention relates to a soft magnetic film and a method of manufacturing the same and a thin-film magnetic head incorporating the soft magnetic film and a method of manufacturing the thin-film magnetic head, and to a head arm assembly and a magnetic disk drive each of which incorporates the thin-film magnetic head.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of magnetic disk drives has increased. A widely used type of thin-film magnetic head is a composite thin-film magnetic head that has a structure in which a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive (MR) element for reading are stacked on a substrate.
The recording systems of magnetic disk drives include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium.
For each of the longitudinal magnetic recording system and the perpendicular magnetic recording system, a write head incorporates: a coil for generating a magnetic field corresponding to data to be written on a recording medium; and a pole layer allowing a magnetic flux corresponding to the field generated by the coil to pass therethrough and generating a write magnetic field for writing the data on the recording medium.
For the write head to achieve higher recording density, particularly required are a reduction in track width, that is, a reduction in width of the end face of the pole layer located in the medium facing surface, and an improvement in write characteristics. However, if the track width is reduced, write characteristics such as an overwrite property that is a parameter indicating an overwriting capability suffers degradation. Therefore, it is required to achieve better write characteristics as the track width is reduced.
To improve the overwrite property, it is required that the pole layer be made of a material having a high saturation flux density. It is also required that the material of the pole layer have an excellent soft magnetic characteristic, that is, a low coercivity. To be specific, it is required that the material of the pole layer have such a characteristic that the saturation flux density is 2.0 T (tesla) or higher and the coercivity is 5.0×79.6 A/m or lower.
One of known materials having a high saturation flux density is an iron-cobalt-nickel alloy. As shown in FIG. 3 of Osaka et al., “Controlling Microstructure of Soft Magnetic Thin Films by the Electrodeposition Method”, Journal of The Magnetics Society of Japan, Vol. 24, No. 11, 2000, pp. 1333-1341, a bulk material of an iron-cobalt-nickel-base alloy exhibits a high saturation flux density.
Conventionally, however, it is difficult to stably achieve such a characteristic that the saturation flux density is 2.0 T or higher and the coercivity is 5.0×79.6 A/m or lower with a soft magnetic film made of an iron-cobalt-nickel-base alloy (such a soft magnetic film will be hereinafter referred to as an FeCoNi film), particularly an FeCoNi film formed by plating. The reason will be described in detail later.
Japanese Published Patent Application (hereinafter referred to as “JP-A”) 2002-134318 discloses a technique of fabricating an FeCoNi film by plating using direct currents through controlling the concentrations of Fe ions, Co ions and Ni ions in a plating bath, thereby suppressing occurrences of pits and cracks in the FeCoNi film.
JP-A 2000-187808 discloses a technique of fabricating an FeCoNi film having a high saturation flux density and a low coercivity by plating through controlling the proportions of Fe, Co and Ni and the proportion of one or two elements selected from P, B, C and N.
JP-A 2002-217029 discloses a technique of fabricating an FeCoNi film having a high saturation flux density and a low coercivity by plating through using pulse currents and controlling the concentrations of Fe ions, Co ions and Ni ions in a plating bath.
JP-A 2003-34891 discloses a technique of fabricating a cobalt-iron-alloy-plated magnetic thin film or a cobalt-iron-molybdenum-alloy magnetic thin film that has a high saturation flux density by plating using bipolar pulse currents.
Japanese Patent No. 2821456 discloses a cobalt-iron-nickel magnetic thin film that is fabricated by electroplating, contains 40 to 70 weight percent cobalt, 20 to 40 weight percent iron, and 10 to 20 weight percent nickel, and has a crystal structure that is a mixed crystal of a γ phase having a body-centered cubic structure and an a phase having a face-centered cubic structure.
As previously described, it is conventionally difficult to stably achieve such a characteristic that the saturation flux density is 2.0 T or higher and the coercivity is 5.0×79.6 A/m or lower with an FeCoNi film formed by plating. The reason will now be described.
It is possible to increase the saturation flux density of an FeCoNi film by increasing the iron content thereof. For an FeCoNi film formed by plating, however, if the iron content is increased, the amount of impurities taken into the FeCoNi film increases, and it is therefore difficult to make the saturation flux density as high as that of a bulk material. It is possible to improve the soft magnetic characteristics of an FeCoNi film by optimizing the impurities content of the FeCoNi film. However, the saturation flux density of the FeCoNi film decreases if the impurities content thereof increases.
As shown in FIG. 3 and FIG. 7 of Osaka et al. mentioned previously, an FeCoNi film having a saturation flux density of 2.0 T or higher typically has a body-centered cubic crystal structure. Therefore, an FeCoNi film having a body-centered cubic crystal structure easily has a high saturation flux density. However, in such an FeCoNi film, crystal grains are likely to be enlarged and the soft magnetic characteristics are thereby likely to be degraded.
In the case of forming an FeCoNi film by plating using direct currents as disclosed in JP-A 2002-134318, the soft magnetic characteristics of the FeCoNi film are likely to be degraded because the crystal grains are likely to be enlarged in the film, and furthermore, it is difficult to obtain a saturation flux density as high as that of a bulk material because a large amount of impurities are taken into the FeCoNi film. The technique disclosed in JP-A 2000-187808 also seems to use direct currents in plating, and it is therefore difficult through this technique, too, to obtain an FeCoNi film having a saturation flux density as high as that of a bulk material. Actually, as is clear from comparison between FIG. 2 of JP-A 2000-187808 and FIG. 3 of Osaka et al., the saturation flux density of the FeCoNi film fabricated through the technique of JP-A 2000-187808 is lower than that of a bulk material.
In the case of forming an FeCoNi film by plating using pulse currents as disclosed in JP-A 2002-217029, it is possible to reduce enlargement of crystal grains and the amount of impurities taken into the film, compared with the case of forming an FeCoNi film by plating using direct currents. However, if comparison is made between FIG. 8 of JP-A 2002-217029 and FIG. 3 of Osaka et al., it is noted that some of the FeCoNi films fabricated through the technique of JP-A 2002-217029 have a saturation flux density lower than that of a bulk material. Furthermore, as shown in FIG. 9 of JP-A 2002-217029, compositions of the FeCoNi film fabricated through the technique disclosed in this publication that allow the coercivity of the film to be 5.0×79.6 A/m or lower are limited to a very narrow range. Because of the foregoing, it is also difficult by using the technique disclosed in JP-A 2002-217029 to stably achieve such a characteristic of an FeCoNi film that the saturation flux density is 2.0 T or higher and the coercivity is 5.0×79.6 A/m or lower.
FIG. 6 of JP-A 2003-34891 shows the relationship between the composition and the easy axis coercivity of a cobalt-iron-molybdenum alloy formed through the technique disclosed in this publication. As shown in FIG. 6 of this publication, there are few cobalt-iron-molybdenum alloys having a coercivity of 7×79.6 A/m or lower while most cobalt-iron-molybdenum alloys have a coercivity higher than 7×79.6 A/m.
Furthermore, as can be seen from FIG. 3 of Osaka et al., it is difficult to achieve a saturation flux density of 2.0 T or higher with a cobalt-iron-nickel magnetic thin film having a composition within the range disclosed in Japanese Patent No. 2821456.